1. Field of the Invention
The present invention relates to an electrodeless lamp system in which a microwave excites an electrodeless lamp for emitting light from the electrodeless lamp, more particularly, to an improved electrodeless lamp system for outputting high energy light from the electrodeless lamp.
2. Prior Art
An electrodeless lamp is lighted as follows. An emission element such as mercury or the like enclosed inside the lamp is excited by a microwave irradiated from a magnetron via an antenna for emitting the light from the lamp.
For example, microwave ovens used as common domestic articles have been known for heating objects such as frozen food or the like around 600 W by using the microwave irradiated from the magnetron. This type of the microwave oven will never be broken by self-heating of the magnetron since the microwave outputted from the magnetron is low energy.
However, when the microwave energy outputted from the magnetron is high energy, such as more than 6 KW (one side 3 KWxc3x972), the following drawback will arise. As shown in FIG. 5, if electric power being supplied to the magnetron is a maximum output, namely, full power at the beginning of starting the lamp for lighting, the microwave is irradiated from the magnetron with maximum power before an emission element such as mercury or a halogen ferrite enclosed inside the lamp is completely vaporized.
FIGS. 6A through 6F each indicate a time-variation of impedance in the electrodeless lamp system respectively. FIG. 6A indicates a change of operating point P for a two-second period of the time (t=0 through 2) that has passed since starting. FIG. 6B indicates a change of operating point P for the next two-second period of the time (t=2 through 4) that has passed after the first two seconds had passed since starting. FIG. 6C indicates a change of operating point P for the next two-second period of the time (t=4 through 6) that has passed after four seconds had passed since starting. FIG. 6D indicates a change of operating point P for the next two-second period of the time (t=6 through 8) that has passed after six seconds had passed since starting. FIG. 6E indicates a change of operating point P for the next two-second period of the time (t=10 through 12) that has passed after ten seconds had passed since starting. FIG. 6F indicates a change of operating point P for the period of the time that 12 seconds (t=0 through 12) has passed since starting.
According to FIGS. 6A through 6F, the more an operating point P is away from a center of Smith chart, the more a reflected wave is generated. In the meantime, the more the operating point P approaches a center of Smith chart, the less the reflected wave is generated. Furthermore, when the operating point P is at the center of Smith chart, the reflected wave is never generated so that a process for lighting the lamp is completed. The case of FIGS. 6A through 6F shows that the lamp is lighted in 5 seconds.
Accordingly, when the emission element enclosed inside the lamp hardly absorbs the microwave irradiated from the magnetron, the microwave is not absorbed into the emission element and is returned to the magnetron as the reflected wave. Thereby, the magnetron is heated by itself due to the reflected wave. Consequently, any parts of inside the magnetron are melted, or a ceramic material covering around a magnetron output-antenna is cracked. These phenomena cause the magnetron to be destroyed.
Energy of the reflected microwave caused by emitting the light from the lamp has been recently increased due to increases in the energy of the light outputted from the electrodeless lamp, that is, electric power being inputted to the magnetron has been increased.
An isolator capable of easily eliminating the reflected wave can be used as a method to prevent a self-heating of the magnetron caused by the reflected wave. However, this solution increases the size of the electrodeless lamp system (lighting tool) and is expensive in price, etc., thus making the solution impractical.
First, there is provided a heat system including a conventional electrodeless lamp disclosed in the Japanese unexamined Patent Publication H09-82112. The heat system is operated in the following manner. A heater voltage is restricted to a lower value than standard value when lighting the lamp (when high voltage is applied) to shorten a warm-up time as much as possible for securing a stable operation when lighting the lamp.
Second, there is provided a heat system disclosed in the Japanese unexamined Patent Publication 2000-21559 operated in following manner. A predetermined value of initial current is set so as to be lower than a predetermined value of input current as a predetermined value of current flowing through a high-voltage power conversion part. The input current of the high-voltage power conversion part is controlled so as to be a predetermined value of initial current when heating operation is started. Then, the rated electric power is utilized to the utmost by restraining the overshoot of input current to reduce the heating time.
Third, there is provided a heat system disclosed in the Japanese unexamined Patent Publication H02-276189 operated in following manner. A voltage value generating in a high voltage circuit is restricted to around a value enough to be applied at the time of normal oscillation of the magnetron until the temperature of a cathode of the magnetron is raised enough to emit a sufficient quantity of electron for oscillation. At the same time, excessive voltage is not generated on the secondary side so that a magnetron is not oscillated even though the temperature of a cathode is raised. Accordingly, the generation of abnormally high voltage can be prevented until the starting of oscillation of the magnetron after the electronic power is applied. Consequently, breakage of high voltage parts and of a switching device can be prevented.
However, any inventions disclosed in each of the aforementioned unexamined patent publications are not to solve the drawback of the magnetron being destroyed by self-heating caused by the reflected wave.
Furthermore, as for the aforementioned phenomenon, a microwave irradiated from the magnetron is returned to the magnetron again as the reflected wave during the period of the moment from when the microwave begins to be irradiated from the magnetron to when the lamp is in a stable condition for lighting. This situation creates a large stress for the magnetron so as to be a large factor for shortening the life span of the magnetron.
A countermeasure against the aforementioned drawback is considered as follows. The microwave begins to be irradiated from the magnetron under the condition that low microwave energy is outputted from the magnetron. For example, an amount of energy sufficient to output the microwave from the magnetron is gradually increased to the maximum value of outputting condition during the period of time from approximately 5 to 20 seconds for lighting the lamp completely. Specifically, the stress applying to the magnetron caused by the reflected wave can be reduced by a soft-starting method. Accordingly, the life span of the magnetron can be expanded.
Therefore, the object of the present invention is to cope with aforementioned drawback for providing the electrodeless lamp system capable of preventing the magnetron from being broken by the self-heating caused by the reflected wave.
To attain aforementioned object, the electrodeless lamp system is comprised in following ways.
As a first aspect of the present invention, a soft-starting method is practiced on the electrodeless lamp system, wherein the electrodeless lamp is excited by an electromagnetic field of the microwave irradiated from the magnetron for emitting the light from the lamp. Herein, the soft-starting method gradually increases electric power enough to drive said magnetron and is used when the light begins to be emitted from the electrodeless lamp.
Accordingly, enough electric power to drive the magnetron can be gradually increased by using the soft-starting method when light begins to be emitted from the electrodeless lamp. Thereby, the electric power being supplied to the magnetron is increased when the emission element enclosed inside the lamp is vaporized. Consequently, the microwave can easily be absorbed into the emission element to reduce the generation of the reflected wave of the microwave, even though a high energy of microwave is outputted from the magnetron.
As a second aspect of the present invention, said soft-starting method according to first aspect of the present invention sets up its timing in the following way. An amount of time until energy of microwave irradiated from the magnetron reaches a maximum value is longer than the amount of time for the emission element in the electrodeless lamp to absorb the microwave and vaporize.
Accordingly, when electric power being supplied to the magnetron reaches a maximum value, the emission element is already vaporized completely. For example, if the amount of time until energy of the microwave irradiated from the magnetron reaches a maximum value is set as approximately 5 through 20 seconds, the lamp is appropriately and perfectly lighted.
As a third aspect of the present invention, a luminous flux density-detecting method is provided during an operation of the operation of the soft-starting method according to the first or second aspect of the present invention. Said detecting method is to detect a luminous flux density of the light irradiated from the electrodeless lamp for controlling an increase of the electric power for being inputted to the magnetron in following ways.
When the light of the luminous flux density detected by the luminous flux density-detecting method is less than a predetermined value, the increase of the electric power for being inputted to the magnetron is stopped for maintaining a waiting condition. On the other hand, when the luminous flux density reaches the predetermined value, the increase of the electric power for being inputted to the magnetron is restarted.
Accordingly, the reflected wave of the microwave can be securely reduced, such that a breakage of the magnetron can securely be prevented.